Community News

Fall bulbs

Brian Kailey

CSU extension agent

Posted:
10/19/2013 10:03:32 AM MDT

Brian Kailey CSU extension agent

September and October are the best months for planting bulbs. This will allow ample time for the bulbs to become well-rooted before the ground freezes. Bulbs planted after October may not have time to root adequately and therefore may not flower uniformly in the spring. Freezing and thawing during the winter may also push an un-rooted bulb out of the ground. Consider mulching the bed to maintain a more consistent soil temperature. Plant the bulbs at a depth consistent with the level indicated on the planting chart. As a general rule, this depth is four times the height of the bulb between the soil surface and the tip of the bulb. Make sure to plant the bulbs with the growing tip up.

After the ground freezes, cover the bed with a 3-inch mulch to prevent alternate freezing and thawing that breaks roots and damages bulbs. This mulch may be removed in April before the shoots emerge, or left in place if the shoots can penetrate it easily.

Figure 1: Bulb planting chart. (Numbers in parentheses refer to minimum spacing.) Lilies normally are planted in the spring, while autumn crocuses normally are planted in midsummer. All other bulbs shown are planted in the fall. Planting depths are for well-drained soils. Bulbs do best in a sandy, clay loam. In heavier soils, plant 1 to 2 inches higher.

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Remove flowers as soon as they wither. The developing seed will divert food produced by the foliage that otherwise would be used to produce more vigorous bulbs. Apply nitrogen at the rate of ¼ pound per 100 square feet before the foliage withers. After the foliage has withered completely, the bulb is dormant. Any additional fertilizer applied after the bulb has become dormant will not be used and wasted.

Bulb beds are usually not dug up after the first year. However, after the second year, the developing bulbs may begin to crowd and lose much of their original vigor, which will result in smaller blooms. When this occurs, dig the bulbs in late August and allow them to dry for a few days in a shady, cool spot. Divide and replant only the best ones, preferably in a new location. If none of the bulbs are as large as the original ones, purchase new bulbs for better results. This is especially true of hyacinths, which are seldom worth transplanting.

When the bulb bed occupies a prominent place in the yard, many growers remove the bulbs after flowering, replacing them with annuals for the summer. It also is possible to interplant annuals among the withering bulb tops. However, do not remove the bulb tops until they are dead. The annuals grow faster and fill in the bed sooner if 5 pounds of 5-10-5 fertilizer per 100 square feet are worked into the soil rather than the ¼ pound of N as suggested previously.

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